The differential batch calorimeter has been modified to eliminate rotational thermal artifacts produced at mixing. FEST indicates chemical reactions with rates slower than 0.2 sec - 1 can be determined with the present analysis. A new thermistor linearizer using a microprocessor has been built and tested with an NBS standardized thermistor accurate to plus 0.01 degrees C. The new instrument has demonstrated the feasibility of this approach but due to front end problems reproducibility at the plus 0.005 degrees C level can only be achieved at 50 microwatts which is too high for cuvette use since the dissipation of the thermistor is 300 microwatts per degree.